Method and system for implementing communications between multiple subnets and MSC

ABSTRACT

The present invention discloses a method and a system for implementing communications between multiple subnets covered by one physical Mobile Switching Center (MSC) and an MSC. The method includes the steps of: mapping one physical MSC to multiple logical MSCs, i.e. multiple virtual MSCs, and assigning a virtual MSC number to each virtual MSC, and setting relationship(s) between location area(s) covered by the virtual MSC and the virtual MSC number of each virtual MSC; transmitting location information of a terminal with the virtual MSC number during communications to implement communications among multiple subnets. During communication, since the terminal location is transmitted according to the virtual MSC number, it is possible to differentiate the terminals located in different subnets covered by a physical MSC, therefore the roaming and handover of the terminal between the subnets can be implemented; and the roaming limitation also can be implemented through the MSC List and VLR List.

FIELD OF THE TECHNOLOGY

The present invention relates to mobile communication technologies, moreparticularly to a method and a system for implementing communicationsbetween multiple subnets covered by a physical Mobile Switching Center(MSC) and an MSC.

BACKGROUND OF THE INVENTION

In networking of mobile communication systems, a local area network ispartitioned and set generally according to geographical locations andthe number of terminals. In areas of sparse population, it is suitableto have a large local area network that covers several small subnets inorder to achieve a closer access and a wide coverage. The large localarea network refers to a network covered by one physical MSC, and it ispartitioned into subnets based on geographical locations to obtain smalllocal area networks.

The large local area network includes a Base Station (BS), a BaseStation Controller (BSC), an MSC, a Visited Location Register (VLR) anda Home Location Register (HLR). The BS (BTS/Node B) receives andtransmits wireless signals, and serves a certain area, and communicateswith terminals in the area. The BTS/Node B is connected with a BaseStation Controller/Radio Network Controller (BSC/RNC), which managesradio resources and controls the base station. The BSC is connected tothe MSC through a Media Gateway (MGW) or directly. The MSC is mainlyused for controlling the mobile calling procedure. The VLR is a databaseto store temporary information of terminals; and the information isneeded when the MSC visits the terminal. The HLR is a database topermanently store management information of the terminals and servicerecords of the terminals.

FIG. 1 shows a network structure which includes three subnets and iscovered by one physical MSC. In FIG. 1, the MSC/VLR covers location area1, location area 2 and location area 3; the location area I furtherincludes two location zones: LAI 11 and LAI 12, the location area 2includes one location zone: LAI 2, and the location area 3 includes onelocation zone LAI 3. It can be seen that the whole network includes onephysical and logical MSC/VLR and one HLR that controls all the terminalsin the network and generates billings and traffic statistic. Theexisting method of distance measurement between a calling party and acalled party is implemented with the MSC/VLR number. Since there is onelogical MSC/VLR, the whole large local area network uses the same MSCnumber. The billing and traffic statistics of terminals communicating indifferent small local area networks, are the same as those of terminalscommunicating in a small local area network.

SUMMARY OF THE INVENTION

The present invention provides a method and a system for implementingcommunications between multiple subnets that are covered by one physicalMobile Switching Center (MSC) and an MSC, so as to differentiateterminals that are located in different subnets covered by one physicalMSC.

The present invention provides a method for implementing communicationsbetween multiple subnets that are covered by one physical MSC, includingsteps of:

mapping one physical MSC to multiple logical MSCs, i.e. multiple virtualMSCs, and assigning a virtual MSC number to each virtual MSC, andrespectively setting a corresponding relationship between a subnetcovered by a virtual MSC and the virtual MSC number of the virtual MSC;

transmitting location information of a terminal with the virtual MSCnumber during communications to implement communications among multiplesubnets.

A system for implementing communications between multiple subnets thatare covered by one physical MSC includes:

virtual MSCs, mapped from one physical MSC, respectively configured witha virtual MSC number and a corresponding relationship between a subnetcovered by the virtual MSC and the virtual MSC number of the virtualMSC; wherein,

the virtual MSC number is used for transmitting location information ofa terminal; and

the virtual MSCs implements communications between multiple subnetsaccording to the virtual MSC number.

An MSC for implementing communications between multiple subnets that arecovered by the MSC includes:

virtual MSCs, mapped from the MSC, respectively configured with avirtual MSC number and a corresponding relationship between a subnetcovered by the virtual MSC and the virtual MSC number of the virtualMSC; wherein,

the virtual MSC number is used for transmitting location information ofa terminal; and

the virtual MSCs implements communications between multiple subnetsaccording to the virtual MSC number.

It can be seen from the scheme mentioned above that, the presentinvention maps one physical MSC into multiple logical MSCs, i.e. virtualMSCs, and assigns MSC numbers for them, and implements communicationsusing the virtual MSC, transmits location information of the terminalaccording to the virtual MSC number during communication, thusimplementing the differentiation of the terminals located in differentsubnets which are covered by one physical MSC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structure diagram of the prior art;

FIG. 2 is a structure diagram illustrating an embodiment of the presentinvention;

FIG. 3 is a signaling flow chart illustrating the procedure of thelocation update according to an embodiment of the present invention;

FIG. 4 is a signaling flow chart illustrating the procedure of assigningthe roaming number;

FIG. 5 is a signaling flow chart illustrating the procedure of assigningthe handover number.

FIG. 6 is a signaling flow chart when the terminal is the called partyin the intelligent service.

DETAILED DESCRIPTION OF THE INVENTION

The problem caused by the related art is it is difficult to determinewhich subnet the terminal currently belongs to according to the MSC/VLRnumber, so it is difficult to accurately bill the terminals based on thedistance within the physical MSC. For example, in FIG. 1 the call madeby the terminal in the location area 2 to the terminal in the locationarea 3 is a long-distance call, but there is one MSC number so it isimpossible to detect that the communication happens between differentlocation areas, which leads to incorrect billing and the trafficstatistics, and it can not be detected that the long-distance call ismade by the location area 2 to the location area 3.

Furthermore, since the same MSC number and the same VLR number are usedin one physical MSC, it is difficult to implement some services, e.g.roaming limitation, etc., by setting the MSC number or VLR number. Forexample, since there is one MSC/VLR number, it is impossible to makesure the terminal in the location area 2 communicates within thelocation area 2 without roaming to other location areas by a VLR list.

To make the scheme, and the advantages of the present invention clearer,the present invention will be described in detail with reference toaccompanying drawings.

A method for implementing communication between multiple subnets coveredby one physical MSC is provided, mainly including the following steps:mapping one physical MSC to multiple logical MSCs, i.e. multiple virtualMSCs, and assigning a virtual MSC number to each virtual MSC, andrespectively setting a corresponding relationship between a locationarea covered by a virtual MSC and the virtual MSC number of the virtualMSC; transmitting location information of a terminal with the virtualMSC number during communications to implement communications amongmultiple subnets. Furthermore, mapping one physical VLR into multiplelogical and virtual VLRs, and assigning a virtual VLR number to eachlogical and virtual VLR; and setting relationships between the virtualMSC number and virtual VLR numbers in a system, so that each virtual MSCcorresponds to one virtual VLR.

In real applications, one location area can correspond to one virtualMSC, but one virtual MSC can correspond to multiple location areas, thespecific relationships can be determined according to differentsituations. While the relationship between the virtual MSC and thevirtual VLR is: one virtual MSC corresponds to at least one virtual VLR,and one VLR can correspond to multiple MSCs.

The first embodiment of the present invention is applied in acommunication system which has the VLR number, e.g. a Global System ofMobile (GSM), Wideband Code Division Multiple Access (WCDMA). As shownin FIG. 2, in the present embodiment, one physical MSC is mapped tothree virtual MSCs, i.e. MSC 1, MSC 2, MSC 3, and one VLR is mapped tothree virtual VLRs, the numbers of them are: VLR 1, VLR 2, and VLR 3,respectively. The relationships among the virtual MSC number, thevirtual VLR number and the location areas are set as follows: the MSC 1corresponds to the VLR 1, the MSC 2 corresponds to the VLR 2, the MSC3corresponds to the VLR 3, the MSC 1/VLR 1 corresponds to the locationareas LAI 11 and LAI 12, the MSC 2/VLR 2 corresponds to the locationarea LAI 2, and the MSC 3/VLR 3 corresponds to the location area LAI 3.

After the step of mapping the multiple virtual MSCs and the multiplevirtual VLRs, the involved communication process includes: locationupdate, assigning the roaming number, assigning the handover number,etc. The communication process will be illustrated hereinafter indetail.

The location update of the terminal will be illustrated by taking theterminal roaming from the MSC 1/VLR 1/LAI 11 to the MSC 2/VLR 2/LAI 2 asan example. As shown in FIG. 3, after the terminal roams to the MSC2/VLR 2/LAI 2, the procedure of the location update is as follows:

Step 301, the terminal sends a location update request, including theinformation of the original location area and the current location area,to the currently visited MSC 2/VLR 2.

Step 302, the currently visited MSC 2/VLR 2 sends the location updaterequest to the HLR of the terminal, and initiates the visiting conflicttimer for the terminal.

In this step, the MSC 2/VLR 2 determines that the original location areais the LAI 11, the current location area is the LAI 2, thus determinesthat the LAI 11 and the LAI 2 correspond to the MSC 1/VLR 1 and the MSC2/VLR 2 respectively according to the relationships among the location,the virtual MSC and the virtual VLR. The MSC 2/VLR 2 sends the locationupdate request, with the MSC 2 number and the VLR 2 number in it, toinform the HLR of the change of the MSC/VLR where the terminal locates.

Step 303, the HLR sends a delete location request to the MSC 1/VLR 1after receiving the location update request from the MSC 2/VLR 2,requesting the MSC 1/VLR 1 to delete the user data corresponding to theterminal.

Step 304, the MSC 1/VLR 1 determines whether a visiting conflict timeris overtime after receiving the delete location request, if the timer isovertime, execute step 305; otherwise, execute step 306. Since the MSC1/VLR 1 and the MSC 2/VLR 2 belong to the same physical MSC/VLR, thetimer initiated in Step 302 is the timer in the physical MSC/VLR and thevisiting conflict timer in this step.

Step 305, the MSC 1/VLR 1 deletes the user data corresponding to theterminal and sends a delete location response to the HLR, and thenexecutes Step 307.

Step 306, the MSC 1/VLR 1 sends a delete location response to the HLR,and then executing Step 307, wherein, the MSC 1/VLR 1 keeps the userdata of the terminal instead of deleting them.

Step 307, the HLR sends an insert user data request to the MSC2/VLR2after receiving the delete location response.

Step 308, the MSC 2/VLR 2 inserts the user data corresponding to theterminal after receiving the insert user data request, and sends aninsert user data response to the HLR, wherein, if the user data is notdeleted in step 306, but the MSC 2/VLR 2 receives the insert user datarequest, then overwrite the original user data, which is not deleted bythe MSC 1/VLR 1, with the new user data.

Step 309, the HLR sends the location update response to the MSC 2/VLR 2.

Step 310, the MSC 2/VLR 2 sends the location update response to theterminal.

In this procedure, if a Super-Charge technique is adopted in thenetwork, the location update request sent by the MSC 2/VLR 2 to the HLRin step 302 includes an information element: Supper-Charge Supported inServing Network Entity. The HLR will not initiate the delete locationprocedure after receiving the request, i.e. not execute step 303 to step308, while directly execute step 309, i.e. directly send the locationupdate response to the MSC 2/VLR 2.

The above-mentioned procedure is the location update procedure after theterminal roams to the destination location area. The procedure ofassigning the roaming number after the terminal roams to the destinationlocation area will be illustrated hereinafter.

When a terminal is called, the call is firstly relayed to the GatewayMobile Switching Center (GMSC) of the terminal, then the GMSC sends arouting request to the HLR of the terminal according to the called partynumber; the HLR needs to assign the roaming number after receiving therouting request. The procedure of assigning the roaming number will beillustrated hereinafter by taking the roaming from the MSC 1/VLR 1 tothe MSC 2/VLR 2 as an example. As shown in FIG. 4, the procedureincludes following steps:

Step 401, the HLR sends a provide roaming number request to the MSC2/VLR 2.

The provide roaming number request message includes the latest MSCnumber, i.e. the MSC 2 number, stored in the HLR by the called terminal,so the physical VLR can take the MSC 2 number as a prefix to assign theroaming number.

Step 402, After the MSC 2/VLR 2 receives the provide roaming numberrequest, the physical VLR assigns a roaming number to the terminal basedon the MSC 2 number.

Step 403, the MSC 2/VLR 2 sends a provide roaming number response to theHLR.

Step 404, the HLR sends an initial address message to the MSC 2/VLR 2.

Step 405, the MSC 2/VLR 2 initiates paging to the called terminal.

The roaming number of the called terminal embodies the logical MSC wherethe called terminal locates after assigning the roaming number, so thebilling center can detect the location of the called terminal withoutany modification.

In addition, to implement the handover billing, the embodiment of thepresent invention assigns the handover number for the terminal duringthe handover between the physical MSC and the virtual MSC or between thevirtual MSCs. For example, during a call, a terminal handover from aneighbor MSC to the virtual MSC 3, add the destination MSC number, i.e.MSC 3 number, to the prepare handover message, so the VLR can assign thehandover number to the terminal based on the MSC 3 number. The specificsteps are as shown in FIG. 5:

Step 501, the neighbor MSC sends a prepare handover request, includinginformation of the destination virtual MSC, i.e. MSC 3, and informationof the destination cell, to the physical MSC/VLR where the MSC 3/VLR 3locates.

Step 502, the physical MSC/VLR sends a handover request to the BaseStation Controller (BSC) that corresponds to the handover destinationcell after receiving the prepare handover request.

Step 503, the BSC sends a handover response to the physical MSC/VLR.

Step 504, the MSC/VLR determines the corresponding location areaaccording to the information of the handover destination cell, and thenindexes to the virtual MSC number, i.e. the MSC 3 number, according tothe location area, and takes the virtual MSC number as the prefix of theassigned handover number.

Step 505, the MSC 3/VLR 3 sends a prepare handover response to theneighbor MSC.

Step 506, the neighbor MSC sends an initial address message to the MSC3/VLR 3.

The above-mentioned is the procedure of assigning the handover number.

In the intelligent service, when the terminal initiates the call at aroaming location, and the terminal is the calling party, the SSP reportsthe currently visited virtual MSC number to the SCP. The SCP can obtainexactly the roaming situation of the calling terminal according to thevirtual MSC number reported by the SSP and the home MSC number of thecalling terminal, and can bill according to the situation.

When the terminal is a called party and the called party is a trigger,then the problem of whether the terminal is roaming is involved. Sincethe terminal is determined to be roaming according to the MSC number andthe VLR number, after the MSC/VLR sends the routing request to the HLR,the HLR returns the virtual MSC number and the virtual VLR number of theterminal during the location update, thus the SCP can obtain the roamingsituation of the called party, and bills based on the situation. Asshown in FIG. 6, the specific steps are as follows:

Step 601, the home virtual MSC of the called terminal sends an obtainingrouting information request, including the called party number, i.e. thecalled terminal number, to the HLR.

Step 602, the HLR obtains the visited virtual MSC number and virtual VLRnumber of the terminal according to the called party number, and returnsa routing information response, including the visited virtual MSC numberand virtual VLR number of the terminal, to the home virtual MSC of theterminal.

Step 603, the home virtual MSC of the called terminal reports thevisited virtual MSC number and virtual VLR number of the called terminalto the SCP.

Therefore, the SCP can bill the called terminal based on the virtual MSCnumber reported by the home virtual MSC.

As to the call statistic, since multiple virtual MSC/VLR numbers areadopted in a large network, the call statistic can be done according tothe virtual MSC/VLR numbers, and can be differentiated by the MSC/VLRnumbers, and the call statistic, roaming statistic and the handoverstatistic can be implemented respectively.

In this embodiment, the limitation method to the roaming terminal isalso included. The limitation can be implemented with the VLR list ofthe terminal. For example, a local service is provided in the urban areaof the city (MSC 1/VLR 1), it is necessary to make sure the terminalapply the local service in the rural area (MSC 2/VLR 2 or MSC 3/VLR 3).This can be done through the following steps: when the terminalinitiates the location update request after roaming to the rural area,the HLR will know the virtual VLR number of the rural area, as seen inthe location update procedure, the HLR compares the virtual VLR numberwith the VLR list of the terminal, determining that the virtual VLRnumber is not in the contracted services, therefore the service of theterminal in this area is limited.

The second embodiment of the present invention is in the communicationsystem without the VLR number. Since the VLR number is only involved inthe procedure of location update and the roaming limitation, themajority of this embodiment is the same as those in the firstembodiment, only the procedures of location update and the roaminglimitation are different, which will be described hereinafter.

In the procedure of the location update, the difference between thisembodiment and the first embodiment is that: in Step 302 of the firstembodiment, the location update request sent by the MSC2/VLR2 to the HLRincludes the virtual MSC2 number.

In the procedure of the roaming limitation, operators can limit theservice of the terminal through the MSC List. For example, a localservice is provided in the urban area of the city (MSC 1/VLR 1), it isnecessary to make sure the terminal apply the local service in the ruralarea (MSC 2/VLR 2 or MSC 3/VLR 3). This can be done through thefollowing steps: when the terminal initiates the location update requestafter roaming to the rural area, the HLR will obtain the virtual VLRnumber of the rural area, as seen in the location update procedure, theHLR compares the virtual VLR number with the VLR list of the terminal,determining that the virtual VLR number is not in the contractedservices, therefore the service of the terminal in this area is limited.

In practical applications, the method of the present invention can beappropriately improved to satisfy the needs of specific scenarios.Therefore, it is understood that the above-mentioned are only thepreferred embodiments of the invention and are not used to confine theprotection scope of the invention.

1. A method for implementing communications between multiple subnetsthat are covered by one physical Mobile Switching Center (MSC),comprising: mapping one physical MSC to multiple virtual MSCs, andassigning a virtual MSC number to each virtual MSC, and setting arelationship between a subnet covered by the virtual MSC and the virtualMSC number of each virtual MSC; and transmitting location information ofa terminal with the virtual MSC number during communications toimplement communications among multiple subnets.
 2. The method accordingto claim 1, wherein the communication procedure in the step oftransmitting location information of a terminal with the virtual MSCnumber comprises: after a terminal roams, assigning a roaming number tothe roaming terminal; a Home Location Register (HLR) sending a provideroaming number request to the virtual MSC to which the terminalcurrently belongs, with the virtual MSC number in the request; and theMSC, to which the terminal currently belongs, assigning a roaming numberto the terminal according to the virtual MSC number after receiving therequest, and sending a provide roaming number response to the HLR. 3.The method according to claim 1, wherein the communication procedure inthe step of transmitting location information of a terminal with thevirtual MSC number comprises: assigning a handover number to theterminal during a handover; an original MSC of the terminal sending aprepare handover request to a destination virtual MSC, wherein theprepare handover request carries information of the destination virtualMSC and information of a destination cell to which the terminal handedover to; and the destination virtual MSC sending a handover request to acorresponding Base Station Controller (BSC) according to the informationof the destination cell; the BSC sending a handover response to thedestination virtual MSC; and the destination virtual MSC obtaining thevirtual MSC number of the destination virtual MSC, and assigning thehandover number by taking the virtual MSC number of the destinationvirtual MSC as a prefix, and sending a prepare handover response to theoriginal MSC.
 4. The method according to claim 1, wherein, during alocation update procedure of the roaming terminal, the communicationprocedure in the step of transmitting the location information of theterminal with the virtual MSC number further comprising: the terminalsending a location update request to the currently visited virtual MSC;the virtual MSC, which is currently visited by the terminal, sending thelocation update request, with virtual MSC number in it, to the HLR ofthe terminal; the HLR of the terminal sending a delete location requestto the original virtual MSC that the terminal visited; the originalvirtual MSC visited by the terminal sending a delete location responseto the HLR after receiving the delete location request; the HLR sendinga insert terminal data request to the virtual MSC, which is currentlyvisited by the terminal, after receiving the delete location response;the virtual MSC currently visited by the terminal inserting the terminaldata after receiving the insert terminal data request, and sending ainsert terminal data response to the HLR; the HLR sending a locationupdate response to the virtual MSC currently visited by the terminal;and the virtual MSC currently visited by the terminal sending thelocation update response to the terminal.
 5. The method according toclaim 1, wherein, when the terminal is a calling party in intelligentservices, the communication procedure in the step of transmitting thelocation information of the terminal with the virtual MSC numbercomprises: the calling party initiates a call, and a Service SwitchingPoint (SSP) reporting the number of the virtual MSC currently visited bythe terminal to a Service Control Point (SCP).
 6. The method accordingto claim 1, wherein, when the terminal is a called party in theintelligent services, the communication procedure in the step oftransmitting the location information of the terminal with the virtualMSC number comprises: the home virtual MSC of the terminal sending arouting information request to the HLR; the HLR obtaining the number ofthe virtual MSC currently visited by the terminal, and sending a routinginformation response, with the number of the virtual MSC currentlyvisited by the terminal, to the terminal; and the home virtual MSC ofthe terminal reporting the number of the virtual MSC of the called partyto the SCP.
 7. The method according to claim 1, wherein the step ofmapping one physical MSC to multiple logical virtual MSCs, and settingrelationship(s) between the location area(s) covered by the virtual MSCand the virtual MSC number of each virtual MSC further comprises:mapping one physical Visited Location Register (VLR) into multiplevirtual VLRs, and assigning a virtual VLR number to each virtual VLR;and setting a relationship between the virtual MSC number and virtualVLR number in a system, so that each virtual MSC corresponds to onevirtual VLR. the step of transmitting the location information of theterminal with the virtual MSC number further comprises: duringcommunication, transmitting the location information of the terminalaccording to the virtual VLR number.
 8. The method according to claim 7,wherein, when the terminal is a called party in the intelligentservices, the step of transmitting the location information of theterminal with the virtual MSC number comprises: the home virtualMSC/virtual VLR of the terminal sending a routing information request tothe HLR; the HLR obtaining the number of the virtual MSC currentlyvisited by the terminal and the virtual VLR number, and sending arouting information response, with the number of the virtual MSCcurrently visited by the terminal and the virtual VLR number in it, tothe terminal; the home virtual MSC/VLR of the terminal reporting thevirtual MSC number and the virtual VLR number of the called party to aService Control Point (SCP).
 9. The method according to claim 7,wherein, during the location update procedure of the roaming terminal,the step of transmitting the location information of the terminal withthe virtual MSC number comprises: the terminal sending a location updaterequest to the currently visited virtual MSC/VLR; the MSC/VLR, which iscurrently visited by the terminal, sending the location update request,with the virtual MSC number and the virtual VLR number in it, to the HLRof the terminal; the HLR of the terminal sending a delete locationrequest to the original virtual MSC/VLR that the terminal visited; theoriginal MSC/VLR visited by the terminal sending a delete locationresponse to the HLR after receiving the delete location request; the HLRsending a insert terminal data request to the virtual MSC/VLR, which iscurrently visited by the terminal, after receiving the delete locationresponse; the virtual MSC/VLR currently visited by the terminalinserting the terminal data after receiving the insert terminal datarequest, and sending a insert terminal data response to the HLR; the HLRsending a location update response to the virtual MSC/VLR currentlyvisited by the terminal after receiving the insert terminal dataresponse; and the virtual MSC/VLR currently visited by the terminalsending the location update response to the terminal.
 10. The methodaccording to claims 4, wherein, after sending the location updaterequest to the VLR of the terminal, further comprising: initiating avisiting conflict timer for the terminal; and after the original virtualMSC receives the delete location request, further comprising:determining whether the visiting conflict timer is overtime; if it isovertime, deleting the user data corresponding to the terminal, and thenexecuting the step of sending the delete location response to the VLR;otherwise, directly executing the step of sending the delete locationresponse to the VLR.
 11. The method according to claims 9, wherein,after sending the location update request to the VLR of the terminal,further comprising: initiating a visiting conflict timer for theterminal; and after the original virtual MSC receives the deletelocation request, further comprising: determining whether the visitingconflict timer is overtime; if it is overtime, deleting the user datacorresponding to the terminal, and then executing the step of sendingthe delete location response to the VLR; otherwise, directly executingthe step of sending the delete location response to the VLR.
 12. Themethod according to claims 4, wherein the location update request thatis sent to the HLR of the terminal comprises: Super-Charge Supported inServing Network Entity; the HLR directly executing the step of sendingthe location update response after receiving the location updaterequest.
 13. The method according to claims 9, wherein, the locationupdate request that is sent to the HLR of the terminal comprises:Super-Charge Supported in Serving Network Entity; then the HLR directlyexecuting the step of sending the location update response afterreceiving the location update request.
 14. The method according to claim7, wherein, the step of mapping one physical MSC to multiple logicalMSCs, and setting relationship(s) between the location area(s) coveredby the virtual MSC and the virtual MSC number of each virtual MSCfurther comprises: setting the VLR number corresponding to the areasthat are permitted to be visited by the terminal in the VLR List of theterminal; in the step of transmitting the location information of theterminal with the virtual MSC number, during transmitting the locationinformation of the terminal according to the virtual VLR number, if itis determined that the virtual VLR number is not in the VLR List of theterminal, restricting the service of the terminal.
 15. A system forimplementing communications between multiple subnets that are covered byone physical Mobile Switching Center (MSC), comprising: virtual MSCs,mapped from one physical MSC, respectively configured with a virtual MSCnumber and a corresponding relationship between a subnet covered by thevirtual MSC and the virtual MSC number of the virtual MSC; wherein, thevirtual MSC number is used for transmitting location information of aterminal; and the virtual MSCs implements communications betweenmultiple subnets according to the virtual MSC number.
 16. The systemaccording to claim 15, further comprising: virtual Visited LocationRegisters (VLRs), respectively configured with a virtual VLR numberwhich is corresponding to a virtual MSC number; wherein, the virtual VLRnumber is used for transmitting location information of a terminal. 17.A Mobile Switching Center (MSC) for implementing communications betweenmultiple subnets that are covered by the MSC, comprising: virtual MSCs,mapped from the MSC, respectively configured with a virtual MSC numberand a corresponding relationship between a subnet covered by the virtualMSC and the virtual MSC number of the virtual MSC; wherein, the virtualMSC number is used for transmitting location information of a terminal;and the virtual MSCs implements communications between multiple subnetsaccording to the virtual MSC number.
 18. The MSC according to claim 17,further comprising: virtual Visited Location Registers (VLRs),respectively configured with a virtual VLR number which is correspondingto a virtual MSC number; wherein, the virtual VLR number is used fortransmitting location information of a terminal.